The Company grants stock-based awards under its 2023 Stock Option and Incentive Plan (the "2023 Plan"), which was approved by the Company’s stockholders in November 2023. The Company also has outstanding stock option awards under the Korro Bio Ops, Inc. 2019 Plan (the "Legacy Korro 2019 Plan"), the Frequency 2014 Stock Incentive Plan (the "2014 Plan"), and the Frequency 2019 Incentive Award Plan (the "Frequency 2019 Plan"), but is no longer granting awards under these plans. The Company also has the option to issue shares under the 2023 Employee Stock Purchase Plan (the "2023 ESPP"), which was approved by the Company’s stockholders in November 2023.

Total stock-based compensation expense recognized in the consolidated statements of operations and comprehensive loss for the three and six months ended June 30, 2025 and 2024 was as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2025		2024		2025		2024
Research and development	$	791	$	334	$	1,421	$	613
General and administrative		1,207		633		2,338		1,219
Total stock-based compensation expense	$	1,998	$	967	$	3,759	$	1,832

The fair value of stock options granted during the six months ended June 30, 2025 and 2024 was calculated on the date of grant using the following weighted-average assumptions:


	Six Months Ended June 30,
	2025			2024
Risk-free interest rate		4.3	%		4.3	%
Expected dividend yield		—	%		—	%
Expected term (in years)		6.0			6.0
Expected volatility		73.6	%		74.6	%

Using the Black-Scholes option pricing model, the weighted-average grant date fair value of stock options granted during the six months ended June 30, 2025 and 2024 was $19.42 and $32.46 per share, respectively.

The following table summarizes changes in stock option activity during the six months ended June 30, 2025 (in thousands, except per share amounts):


	Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2024		1,248,288		$	25.42		8.0	$	21,313
Granted		670,265		$	28.66
Exercised		(13,583	)	$	13.03
Forfeited		(115,741	)	$	29.26
Cancelled		(6,998	)	$	21.08
Outstanding as of June 30, 2025		1,782,231		$	26.50		8.2	$	208
Exercisable at June 30, 2025		689,806		$	24.94		6.7	$	208

The aggregate intrinsic value of options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the common stock as of the end of the period. The aggregate intrinsic value of stock options exercised during the six months ended June 30, 2025 and 2024 was $0.3 million and $0.4 million, respectively.